FIG. 1.

The urease gene cluster of H. pylori parental strains N6 and SS1 and of the derived mutants deficient in UreI, strains N6-823, N6-834, and SS1-834. The genes are indicated by boxes with arrows showing the direction of their transcription. The distances between the ure genes are given in base pairs. The sites hybridizing to the primers used to confirm correct allelic exchange in strains N6-823, N6-834, and SS1-834 are shown. Blank boxes represent the cassettes containing the genes conferring resistance to CM (cat) or to KM (aphA-3). The urease activities of these strains are given on the right side of the figure. Urease activity was measured at pH7 as the release of ammonia in crude extracts of bacteria grown for 48 h on blood agar plates as described previously (8). One unit corresponds to the amount of enzyme required to hydrolyze 1 μmol of urea/min/mg of total protein. The data are means ± standard deviations calculated from three to five determinations.